date: Implement setting the date on Unix & Windows

[marcosatti]

Fixes #1754

Implements basic functionality for setting the date under both Unix & Windows systems.

Unresolved issues:

• parse_date only accepts limited formats for the dates input - separate issue needed?
• How are leap seconds handled on Windows? Not immediately clear, seems like they kind of ignore it which is what I've put in.

[sylvestre]

It would be great to add tests too.
I guess it requires root but we could:

• test that the parsing of the input works
• test that the parsing of the input fails with the right error
• setting the date as not root fails the expected way :)

thanks

[sylvestre]

Has some builds failures!

[marcosatti]

Has some builds failures!

Yeah not quite completed yet...

The 32-bit platforms are still using long as time_t's, so I'll jut add in a try_into() call - they should be updated by 2038 I would hope. The nanoseconds can fit into a i32 no matter what, so a static cast should be fine there.

[marcosatti]

The gnu date always outputs the current date (regardless if there was a permissions error) when setting the date - do you want to create a new issue for this or should it be done in this one?

[marcosatti]

Damn, try_into() was added in a later Rust version (v1.34?)... I'll just use a normal cast.

[sylvestre]

please run

cargo +1.33.0 update

[sylvestre]

only minor requests!
thanks

[sylvestre]

@marcosatti ping?

[marcosatti]

@sylvestre sorry been busy lately - will look at it later on in the week.

[sylvestre]

Looks great :)
I will merge yet now, please open a PR for the last request!

[marcosatti]

Created PR #1846 for more tests.